1. Field of the Invention
The present invention relates to a diagnostic device for electric mechanism drive circuits for diagnosing drive circuits of electric mechanisms including motors, and more particularly to a diagnostic device for electric mechanism drive circuits which diagnoses the state of an electric mechanism when the electric mechanism is to operate and the state of connection between the electric mechanism drive circuit and the electric mechanism, and thereby prevents the electric mechanism from running into trouble or being burnt.
2. Description of the Related Art
Known motor drive circuits according to the prior art for driving a motor for bidirectional revolutions include one having a pair of relays each provided with a normally closed contact, a normally open contact, a movable contact and a drive coil for switching over and driving the movable contact, and a control section supplying the drive coils of the relays with switching signals for switching over their movable contacts. In this motor drive circuit, both normally closed contacts are connected to a grounding point (reference potential point), both normally open contacts are connected to a power supply terminal and both terminals of the motor are connected between the two movable contacts. In response to a switching signal from the control section, if the movable contact of one relay is switched over towards the normally open contact, the motor is driven for revolution in one direction (forward direction), or if the movable contact of the other relay is switched over towards the normally open contact, the motor is driven for revolution in the other direction (reverse direction).
This kind of motor drive circuit, when it is to drive a motor, if there is any trouble in the motor itself, such as short circuiting between terminals, disconnection of a coil or the like, or any trouble in wiring for connecting the motor and a pair of relays, such as short circuiting between lines, disconnection or the like, will not only be unable to normally drive the motor but even invite a major accident, such as burning of the motor. In view of this risk, a diagnostic device for predicting any possible trouble in the motor or its connection wiring is used.
FIG. 4 here is a circuit diagram showing one example of configuration of such a known diagnostic device for motor drive circuits.
As shown in FIG. 4, this motor drive circuit diagnostic device is provided with a control unit 40 made up of a microcomputer having an operation controller 40(1) for controlling the overall operation and a diagnostic section 40(2) and the like; a motor 41 constituting a load; a first relay 42 having a movable contact 42(1), a normally closed contact 42(2), a normally open contact 42(3) and a drive coil 42(4); a second relay 43 having a movable contact 43(1), a normally closed contact 43(2), a normally open contact 43(3) and a drive coil 43(4); a first transistor drive circuit 44 which has a first transistor 44(1) and drives the first relay 42; a second transistor drive circuit 45 which has a second transistor 45(1) and drives the second relay 43; a first connection wiring section 46 having connection terminals 46(1) and 46(2) for connecting one end of the motor 41 and the first relay 42; and a second connection wiring section 47 having connection terminals 47(1) and 47(2) for connecting the other end of the motor 41 and the second relay 43. It is further provided with a switching circuit 48 having a field effect transistor 48(1); a first resistance voltage dividing circuit 49 made up of two series resistors 49(1) and 49(2); a second resistance voltage dividing circuit 50 made up of two series resistors 50(1) and 50(2), and a power supply terminal 51.
One end of the motor 41 is connected to the first connection wiring section 46, and the other end, to the second connection wiring section 47. In the first relay 42, the movable contact 42(1) is connected to the first connection wiring section 46, the normally closed contact 42(2), to the drain of the field effect transistor 48(1), the normally open contact 42(3), to the power supply terminal 51, one end of the drive coil 42(4), to the power supply terminal 51 and the other end, to the collector of the first transistor 44(1). In the second relay 43, the movable contact 43(1) is connected to the second connection wiring section 47, the normally closed contact 43(2), to the drain of the field effect transistor 48(1), the normally open contact 43(3), to the power supply terminal 51, one end of the drive coil 43(4), to the power supply terminal 51 and the other end, to the collector of the second transistor 45(1). In the first transistor drive circuit 44, the base of the first transistor 44(1) is connected to the operation controller 40(1) via a series resistor (no reference numeral assigned) and grounded via a base resistor (no reference numeral assigned) and a shunt capacitor (no reference numeral assigned), and the emitter of the same is directly grounded. In the second transistor drive circuit 45, the base of the second transistor 45(1) is connected to the operation controller 40(1) via a series resistor (no reference numeral assigned) and grounded via a base resistor (no reference numeral assigned) and a shunt capacitor (no reference numeral assigned), and the emitter of the same is directly grounded.
In the switching circuit 48, the gate of the field effect transistor 48(1) is connected to the operation controller 40(1) and grounded via a resistor (no reference numeral assigned), and the source of the same is directly grounded. In the first resistance voltage dividing circuit 49, one end of the resistor 49(1) is connected to the first connection wiring section 46, and the other end of the same is connected to the diagnostic section 40(2) and to one end of the resistor 49(2). One end of the resistor 49(2) is connected to the diagnostic section 40(2), and the other end of the same is grounded. In the second resistance voltage dividing circuit 50, one end of the resistor 50(1) is connected to the second connection wiring section 47 and the other end of the same is connected to the diagnostic section 40(2) and to one end of the resistor 50(2). One end of the resistor 50(2) is connected to the diagnostic section 40(2) and the other end of the same is grounded.
The motor drive circuit diagnostic device of the configuration described above operates as described below.
When the motor 41 is to be revolved in the forward direction, first an ON signal is supplied from the operation controller 40(1) to the field effect transistor 48(1) of the switching circuit 48 to turn on the field effect transistor 48(1); next an ON signal is supplied from the operation controller 40(1) to the first transistor 44(1) of the first transistor drive circuit 44 to turn on the first transistor 44(1); and a drive current is fed to the drive coil 42(4) of the first relay 42. Then the movable contact 42(1) is switched over from the normally closed contact 42(2) side to the normally open contact 42(3) side, and a current flows from the power supply terminal 51 to a grounding point via the first connection wiring section 46, the motor 41 and the second connection wiring section 47 thereby to revolve the motor 41 in the forward direction.
On the other hand, when the motor 41 is to be revolved in the reverse direction, first an ON signal is supplied from the operation controller 40(1) to the field effect transistor 48(1) of the switching circuit 48 to turn the field effect transistor 48(1); next an ON signal is supplied the operation controller 40(1) to the second transistor 45(1) of the second transistor drive circuit 45 to turn on the second transistor 45(1), and a drive current is fed to the drive coil 43(4) of the second relay 43. Then the movable contact 43(1) is switched over from the normally closed contact 43(2) to the normally open contact 43(3), and a current flows from the power supply terminal 51 to the grounding point via the second connection wiring section 47, the motor 41 and the first connection wiring section 46 thereby to revolve the motor 41 in the reverse direction.
When the motor 41 is driven to revolve in this way, the first resistance voltage dividing circuit 49 divides the voltage generated in the first connection wiring section 46 between the resistor 49(1) and the resistor 49(2), and supplies the divided voltages to the diagnostic section 40 (2). Similarly, the second resistance voltage dividing circuit 50 divides the voltage generated in the second connection wiring section 47 between the resistor 50(1) and the resistor 50(2), and supplies the divided voltages to the diagnostic section 40(2). The diagnostic section 40(2) monitors the divided voltages supplied from the first resistance voltage dividing circuit 49 and the second resistance voltage dividing circuit 50 and, if any of those divided voltages becomes abnormal, for instance if at a timing when the first connection wiring section 46 or the second connection wiring section 47 is to be supplied with a source voltage, which is the voltage from the power supply terminal 51 (when the motor 41 is to be driven for revolution), is not supplied with a divided voltage matching that source voltage, i.e. if the divided voltage is found failing to reach a first comparative voltage matching the preset source voltage, it will be diagnosed that there is either disconnection or ground fault in the first connection wiring section 46 or the second connection wiring section 47, or if no ground voltage is supplied to the first connection wiring section 46 or the second connection wiring section 47 at the timing it should be supplied (when the motor 41 is at halt) and instead any divided voltage is supplied, i.e. if the divided voltage is compared with a second comparative voltage matching a preset ground voltage and found surpassing the second comparative voltage, it will be diagnosed that there has arisen short circuiting (short circuiting between the motor 41 and the power supply terminal 51, i.e. between the first connection wiring section 46 and the second connection wiring section 47) in the first connection wiring section 46 or the second connection wiring section 47, and the abnormal state is notified by giving a pertinent indication on a display unit (not shown), lighting an alarm lamp and/or sounding an alarm buzzer.
Further, if an OFF signal is supplied from the operation controller 40(1) to the field effect transistor 48(1) of the switching circuit 48 in a short period of time immediately after the drive to revolve the motor 41 has ended to turn off the field effect transistor 48(1), even if short circuiting has arisen in the first connection wiring section 46 or the second connection wiring section 47, the source voltage of the first connection wiring section 46 or the second connection wiring section 47 in a short-circuited state will not flow to the grounding point via the field effect transistor 48(1), and accordingly no drive current will flow to the motor 41 or any other circuit element, so that the motor 41 can be prevented from burning or other circuit elements from being damaged otherwise.
In the known motor drive circuit diagnostic device described above, it is possible to diagnose the presence or absence of abnormality in any part, such as disconnection, ground fault or short circuiting when the motor 41 is being driven by connecting the switching circuit 48 to the normally closed contacts 42(2) and 43(2) of the first and second relays 42 and 43, the first resistance voltage dividing circuit 49 to the first connection wiring section 46 and the second resistance voltage dividing circuit 50 to the second connection wiring section 47, but this diagnosis in any case is accomplished after the motor 41 is set in a driven state. If the motor 41 is set in a driven state when there is disconnection, ground fault or short circuiting, even if it is driven for only a short period of time, a large current may flow momentarily to some part, and this could damage the motor drive circuit in some way or other.
An object of the present invention, attempted in view of the technical background described above, is to provide a diagnostic device for electric mechanism drive circuits enabled to perform diagnoses not only when the electric mechanism is being driven but also when the electric mechanism is not driven.
In order to achieve the object above, a diagnostic device for electric mechanism drive circuits according to the present invention comprises:
a drive circuit, provided with a pair of relays connected to an electric mechanism and a switching circuit connected between normally closed contacts of the pair of relays and a reference potential point, for driving the electric mechanism,
an operation controller for regulating the drive circuit to control operation of the electric mechanism,
voltage dividing circuits connected between the electric mechanism and the drive circuit, and
a diagnostic section for diagnosing a state of supply of drive power to the electric mechanism on the basis of voltage-division outputs of the voltage dividing circuits, wherein
a bias voltage supply circuit is provided to supply a bias voltage between connection points between the normally closed contacts of the pair of relays and the switching circuit,
an additional voltage dividing circuit is connected between the connection point and the reference potential point, and
the diagnostic section diagnoses a connection state of the electric mechanism and the drive circuit, in a state in which the switching circuit is turned off, on the basis of the voltage-division outputs of the additional voltage dividing circuit.
This configuration according to the invention makes possible diagnosis of the presence or absence of disconnection, ground fault or short circuiting not only when an electric mechanism is driven by connecting a switching circuit and first and second voltage dividing circuits as known diagnostic devices for electric mechanism drive circuits according to the prior art do, but also when the electric mechanism is not driven by supplying a bias voltage to the connection point between a pair of normally closed contacts and the switching circuit, connecting an additional resistance voltage dividing circuit between the connection point and a reference potential point, and causing the diagnostic section to diagnose the voltage-division outputs of the additional resistance voltage dividing circuit in a state in which the switching circuit is turned off.
The diagnostic device for electric mechanism drive circuits according to the invention may have, in addition to the above-described configuration, a capacitance element constituting an integrating circuit connected between a voltage division point and the reference potential point in the additional voltage dividing circuit.
This makes possible satisfactory diagnosis even if noise arises at the voltage division point because the noise would flow to the reference potential point through the capacitance element, and the noise entering into the diagnostic section can be substantially reduced thereby.
The diagnostic device for electric mechanism drive circuits according to the invention may have, in addition to the above-described configuration, a constant voltage setting element connected between the voltage division point and the reference potential point in the additional voltage dividing circuit.
This configuration makes possible satisfactory diagnosis because the constant voltage characteristics of the constant voltage setting element serve to remove noise.